This invention relates to magnetic recording media, more particularly rigid or hard disk media, wherein the magnetic recording material is patterned on the disk into discrete regions of single magnetic domains, each domain corresponding to the storage of a single data bit.
Conventional hard disk drives typically use a continuous granular magnetic film as the recording medium. Each magnetic bit is comprised of many small magnetized grains. The difficulty in controlling the size, composition, and shape distribution of the grains in such media is compounded by the dichotomy associated with tuning the degree of magnetic coupling between the magnetic grains, i.e., weakening the magnetic coupling sharpens the transition between adjacent magnetic bits, while strengthening the magnetic coupling improves the recording characteristics of the individual magnetic bits.
The challenge of producing granular media will grow with the trend toward higher areal storage densities. Reducing the size of the magnetic bits while maintaining a satisfactory signal-to-noise ratio, for example, requires decreasing the size of the grains. Unfortunately, significantly reducing the size of weakly coupled magnetic grains will make their magnetization unstable (i.e., superparamagnetic) at normal operating temperatures. To postpone the arrival of this fundamental limit and to avert other difficulties associated with extending granular media, there has been renewed interest in patterned magnetic media.
With patterned media, the continuous granular magnetic film that covers the disk substrate is replaced by an array of spatially separated discrete magnetic regions, each of which serves as a single magnetic bit. Since this approach forcibly creates a well-defined boundary between adjacent bits, the problem of minimizing the transition width between adjacent bits is largely decoupled from the problem of optimizing the recording properties of the bits themselves. As a result of this increased latitude for bit design, each bit can be comprised of fewer and larger grains, the magnetic anisotropy of the grains can be increased, and the magnetic coupling between grains can be strengthened. These design tactics will likely push the onset of superparamagnetic behavior at normal operating temperatures to significantly higher areal densities.
The primary approach in the prior art for producing patterned media has been to selectively deposit or remove magnetic material from a magnetic layer on the substrate so that magnetic regions are isolated from one another and surrounded by areas of non-magnetic material. There are a variety of techniques for the selective deposition or removal of magnetic material from a substrate. In one technique the substrate is covered with a lithographically patterned resist material and a magnetic film is then vacuum deposited to blanket both the areas of resist and the areas of exposed substrate. The resist is then dissolved to lift off the magnetic film that covers it, leaving an array of isolated magnetic regions. An alternative technique is to first deposit a magnetic film on the substrate and then pattern resist material on the magnetic film itself. Magnetic material from the areas not protected by the resist can then be selectively removed by well-known processes. Examples of patterned magnetic media made with these types of lithographic processes are described in U.S. Pat. Nos. 5,587,223; 5,768,075 and 6,820,769.
From a manufacturing perspective, an undesirable aspect of the lithographic process is that it requires potentially disruptive processing with the magnetic media in place. Processes required for the effective removal of resists and for the reliable lift-off of fine metal features over large areas can damage the material left behind and therefore lower production yields. Also, these processes must leave a surface that is clean enough so that the magnetic read/write head supported on the air-bearing slider of the disk drive can fly over the disk surface at very low flying heights, typically below 30 nanometers (nm).
What is needed is a process of making a patterned magnetic recording disk that does not suffer from the disadvantages of the lithographic processes to selectively remove and/or deposit material on the substrate.
The invention is a method for making a patterned magnetic recording disk by patterned ion implantation of the disk substrate. Energetic ons, such as He, N or Ar ions, are directed to the disk substrate through a mask, preferably a non-contact mask. The ions implant into the substrate and the process causes localized topographic distortions in the substrate surface. A magnetic layer is then deposited over the substrate in the conventional manner, such as by sputtering. The result is a disk with patterned magnetic regions that are raised above the substrate surface. Because these regions are elevated, they are closer to the recording head in the disk drive and can thus be individually recorded to form discrete magnetic bits. In one embodiment the ion implantation causes localized expansion or swelling in the substrate material to form pillars that are elevated above the substrate surface. The patches of magnetic material on the tops of the pillars form the discrete magnetic bits.
In another embodiment the ion implantation causes localized compaction in the substrate material to form pits in the substrate surface. The magnetic material deposited in the regions between the pits is higher and thus serves as the discrete magnetic bits. In a variation of this embodiment, the disk is polished after the magnetic layer is formed to remove magnetic material in the regions between the pits, so that the resulting disk has a generally planar surface with the magnetic material formed only in the pits. The completed magnetic recording disk differs from prior art patterned magnetic recording disks because the substrate has localized topographic distortions relative to the rest of the substrate surface with these distortions containing concentrations of chemical species caused by the implanted ions that are not present in the regions of the substrate that have been masked from the ion irradiation.
In addition to being patterned with the individually recordable data bits for use as user data, the disk can also be patterned with magnetic bits that are used to later form discrete pre-recorded bits for servo tracking information and track and sector identification information.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.